(1. ) Field of the Invention
The present invention relates to an aluminum type metal-based composite material comprising an aluminum borate whisker as a reinforcer, and a process for the preparation thereof.
(2) Description of the Related Art
With recent technical development in various industries represented by the aerospace industry, the demand for a new material having higher strength, elasticity and hardness and capable of resisting a higher temperature than conventional metal materials is increasing.
Among metal materials, aluminum and aluminum alloys have a low specific gravity and an easy workability and are supplied at low costs, and therefore, they are widely used as materials having high strength and heat resistance in various fields for airplanes, automobiles, construction materials, chemical machines and the like.
As the means for improving the mechanical properties of aluminum type metals, there have been vigorously investigated methods of forming composite materials by combining an aluminum type alloy with a whisker or fiber of a material having high strength and elasticity, such as silicon carbide, silicon nitride, carbon, alumina or potassium hexatitanate, as a whisker or reinforcer, and as the composite-forming method, there are known a hot press method, a HIP method, an infiltration method, a powder metallurgy method, a high-pressure casting case method and a hot extrusion method.
In the production of an aluminum type metal-based composite material, it is important that a reinforcing whisker or fiber should have a high wettability with and be inert to a melt of aluminum. However, reinforcers having such properties are limited in number and most of whiskers and fibers are practically used in the state where the surface is coated with an inert compound.
Among these reinforcers, an alumina type fiber or whisker and a silicon carbide whisker satisfy the above-mentioned two-requirements and are promising as a reinforcing material. However, since they are expensive, they can hardly be applied to general-purpose uses for automobiles, construction materials and the like, though they may be used in the aerospace industry.
At the present, from the economical viewpoint, only a whisker of potassium hexatitanate can be used as a general-purpose reinforcer for the production of an aluminum type metal composite material. However, this compound has an inherent problem in that tetravalent titanium is reduced with metallic aluminum and an intermetallic compound such as Ti.sub.3 Al is formed.
Accordingly, this reducing reaction is controlled by shortening the heat treatment time to the utmost, but in this case, the process becomes defective in that no satisfactory composite effect can be attained.